GCSE Physics resources
AQA GCSE Magnetism and electromagnetism
The National Grid’s purpose is common course content. Both courses Higher use ideal-transformer power equality; transformer construction, induction and turns ratio are Physics Higher.
Subsection scope: National Grid and efficient transmission: both courses, both tiers. Ideal-transformer power equality: both courses Higher. Transformer mechanism and turns ratio: Physics Higher only.
Start here
The National Grid’s purpose is common course content. Both courses Higher use ideal-transformer power equality; transformer construction, induction and turns ratio are Physics Higher.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
The National Grid’s purpose is common course content. Both courses Higher use ideal-transformer power equality; transformer construction, induction and turns ratio are Physics Higher.
Scope: 8463 and 8464 · Foundation and Higher
The Grid links generators and consumers through cables and transformers. Step-up transformers raise transmission voltage; step-down transformers lower it for users. At fixed transmitted power P = VI, raising V lowers I. For the same cable resistance, Pheat = I²R then decreases. Raising voltage is useful for efficient transmission but requires insulation and step-down stages for use.
Scope: 8463 Physics only · Higher only
An alternating current in the primary coil creates a changing magnetic field in an iron core. This changing field reaches the secondary and induces p.d. A steady direct current creates no continuously changing field, so no continuous secondary output. Vₛ/Vₚ = Nₛ/Nₚ; the larger-turn coil has the larger p.d. The iron core links fields and is easily magnetised.
Scope: 8463 and 8464 · Higher only
For an ideal transformer, VₚIₚ = VₛIₛ. Both Physics and Trilogy Higher use this equality. Stepping voltage up steps current down for equal power. If input is 12 V and secondary output is 6 V at 0.50 A, output power is 3 W and ideal primary current is 3/12 = 0.25 A. No turns data are needed for this calculation. Real transformers have losses, so input power exceeds output.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Higher current and more heating.
Use instead: P = VI requires lower I when V rises. This is the Grid efficiency chain.
Tempting idea: 96 V.
Use instead: That reverses the turns ratio. 24 × 100/400 = 6.
Retrieval practice
Explore the relationship
Change primary voltage or the secondary:primary turns ratio, then use Vₛ = Vₚ × (Nₛ ÷ Nₚ).
Model scope: 8463 Physics only · Higher only
What to notice: use the readout to describe how one variable changes when the other is controlled.
Worked examples
Apply national grid and high-voltage transfer in the worked reasoning, then try the changed-context questions below.
Scope: 8463 Physics only · Higher only
Vs = 1150 V.
Scope: 8463 and 8464 · Foundation and Higher
Lower current reduces energy transferred to thermal stores of cables due to resistance.
Scope: 8463 Physics only · Higher only
A steady current does not continually change the magnetic field, so no continuous p.d. is induced in the secondary coil.
Exam precision
Do this: For Grid losses hold transmitted power and cable resistance fixed. Check the course label before using power equality or the Physics turns ratio.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): For fixed power, P = VI means higher V permits lower I. Point 2 (1 mark): Lower I reduces heating loss in the same resistive cables. Point 3 (1 mark): Step-down transformers then reduce voltage for consumers. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: High voltage lowers current for the required power and reduces cable heating. Step-down transformers make the voltage suitable for consumers.
Scope: 8463 Physics only · Higher only
Original PhysicsUK mark scheme: Point 1 (1 mark): Vs/Vp = Ns/Np. Point 2 (1 mark): Vs = 12 × 150/600. Point 3 (1 mark): Vs = 3.0 V. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Vs/Vp = Ns/Np. Vs = 12 × 150/600. Vs = 3.0 V.
Acceptable answers: Expected result: Vs = 3.0 V. Accept the unrounded value or a correctly rounded equivalent to two or more significant figures; accept equivalent units if converted correctly. No additional measurement interval is implied.
Marking notes: Method marks remain available after an arithmetic error. Carry an earlier numerical error into a later valid step; award that method point if the unit conversion and physics are correct. A fully correct answer with unit earns all marks unless working is expressly requested.
Scope: 8463 and 8464 · Higher only
Original PhysicsUK mark scheme: Point 1 (1 mark): VpIp = VsIs; Ip = VsIs/Vp. Point 2 (1 mark): Ip = 6 × 0.50/12. Point 3 (1 mark): Ip = 0.25 A. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: VpIp = VsIs; Ip = VsIs/Vp. Ip = 6 × 0.50/12. Ip = 0.25 A.
Acceptable answers: Expected result: Ip = 0.25 A. Accept the unrounded value or a correctly rounded equivalent to two or more significant figures; accept equivalent units if converted correctly. No additional measurement interval is implied.
Marking notes: Method marks remain available after an arithmetic error. Carry an earlier numerical error into a later valid step; award that method point if the unit conversion and physics are correct. A fully correct answer with unit earns all marks unless working is expressly requested.
Questions pupils ask
Raising voltage lowers current for the same transmitted power, reducing resistive I²R heating of the cables.
Useful next steps